All Out Attack (5e Variant Rule)
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Named after the combat mechanic from the Persona franchise.
An all-out attack can only be initiated when a target is unable to move in any direction. A creature must use their entire turn (including action, bonus action, movement, etc) to initiate the all-out attack. All creatures with the target within reach may attack the target as a reaction. This is a very powerful mechanic that is advised to use with caution.